The present invention relates to a method of epitaxial growth of a silicon layer on a silicon substrate and an apparatus therefor, and more particularly to a method of removal of a carbon-contaminated layer from a silicon substrate surface for subsequent selective silicon epitaxial growth on the silicon substrate surface and an apparatus therefor.
FIG. 1 is a schematic diagram illustrative of a structure of the conventional silicon epitaxial growth system provided with a deep ultraviolet ray generator for generating chlorine radicals to remove carbon contamination. The silicon epitaxial growth system comprises the following elements. A growth chamber 2 is adopted for accommodating a silicon substrate 1 and epitaxially growing a silicon layer on the silicon substrate 1. A heater chamber 3 is provided adjacent to the growth chamber 2 so that the heater chamber 3 is positioned under the silicon substrate 1, whilst the growth chamber 2 is positioned over the silicon substrate 1. Namely, the heater chamber 3 is separated by the silicon substrate 1 from the growth chamber 2. In the heater chamber 3, a substrate heater 4 serving as a substrate temperature controller is provided for controlling a temperature of the silicon substrate 1 or heating up the silicon substrate 1. In the growth chamber 2, the silicon substrate 1 is supported by a suscepter 5. A pair of turbo molecular pumps 6 are provided which are coupled with the growth chamber 2 and the heater chamber 3 respectively for differential discharge. A silane system gas feeding tube 9 is provided to be connected to the growth chamber 2 for supplying a silane system gas such as a silane gas and a disilane gas into the growth chamber 2 for epitaxial growth of the silicon layer on the silicon substrate 1. A chlorine radical generator is furthermore provided to be connected to the growth chamber 2 for generating a chlorine radical and supplying the chlorine radical onto the silicon substrate 1 in the growth chamber 2. The chlorine radical generator comprises a chlorine gas feeding tube 10, through which a chlorine gas is fed, a deep ultraviolet ray generator 17 provided on a side wall of the growth chamber 2. The level in position of the deep ultraviolet ray generator 17 is higher than the level of the silicon substrate 1 and lower than the level of the chlorine gas feeding tube 10 so that the deep ultraviolet ray generator 17 generates a deep ultraviolet ray to be irradiated to the chlorine gas fed from the chlorine gas feeding tube 10 whereby the chlorine gas is made into chlorine radical but at a lower efficiency. On the other hand, the silane system gas feeding tube 9 is provided at an oblique angle to the surface of the silicon substrate 1 so that the silane system gas is injected into the growth chamber 2 at the oblique angle to the surface of the silicon substrate 1. The above device is disclosed in the Japanese laid-open patent publication No. 63-237419.
The chlorine radical is irradiated to the silicon substrate surface to remove a carbon-contamination from the silicon substrate surface. Notwithstanding, actuary, carbon resides on the silicon substrate surface 1 at a certain high sheet concentration in the order of 1.times.10.sup.14 /cm.sup.2 because when the deep ultraviolet ray is used to generate chlorine radical, generation efficiency of the chlorine radical is too low, for example, not more than 0.5%, resulting in a too small an amount of the generated chlorine radical to be irradiated onto the carbon-contamination on the silicon substrate surface. This results in a too low etching rate of etching the carbon-contaminated layer over the silicon substrate surface.
If in order to increase the etching rate or obtain a sufficient amount of the chlorine radical, it is required to increase the chlorine gas pressure up to 0.1 torr or more. The above silicon epitaxial growth system is designed so that a background pressure in no gas flow condition is in the range of 1.times.10.sup.-9 -1.times.10.sup.-10 torr whilst an operational gas pressure in a certain gas flow condition is not more than 5.times.10.sup.14 torr. If the gas pressure were greater than the above maximum values, then the system will receive a considerable load resulting in shortening its life-time. Namely, the maximum gas pressure of 5.times.10.sup.-14 torr is insufficient to obtain the necessary amount of the chlorine radical to completely remove the carbon-contaminated layer from the silicon substrate surface.
In the above circumstances, it had been required to develop a novel method and an apparatus for removing the carbon-contaminated layer from the silicon substrate surface without, however, raising the above problems.